The present invention is a light mixer for use in connection with an optical probe of a spectrophotometric-type instrument. In particular, the invention is a mixer for combining the different wavelength light beams from a plurality of discrete optical fibers into a homogeneous beam prior to transmission into tissue being analyzed.
Spectrophotometric-type instruments are known and used in a variety of applications. An instrument of this type is, for example, disclosed in the Anderson et al. U.S. Pat. No. 5,879,294. These instruments transmit light at a number of predetermined wavelengths through the tissue being measured, and then collect and process the light. Measurements of the tissue parameters of interest are generated as a function of the attenuation of the light at these wavelengths by the tissue. Several different approaches for obtaining the different wavelength light signals are used. One approach is to transmit through and collect from the tissue broad bandwidth light, and to separate the different wavelength signals from the collected light prior to processing. Another approach is to use light emitting diodes (LEDs) or other sources to generate narrow bandwidth light beams (i.e., signals at the wavelengths of interest). These narrow bandwidth beams are then individually transmitted to the tissue being measured by separate individual optical fibers sometimes referred to as send fibers. A drawback of the use of individual send fibers is that light from one or more of these fibers may be attenuated differently than the light from other fibers due to inhomogeneities on the surface of the tissue where the light exits the send fibers and is transmitted into the tissue (i.e., the tissue target). This drawback is possible even though the ends of the send fibers are located adjacent to one another. For example, the end of one of the fibers could be over a mole or hair, while the others are not. Inaccurate measurements can result from these circumstances.
A number of approaches for combining light from individual optical fibers are known. One approach is to fuse the individual fibers into a common fiber. Another approach is to fixture the LEDs onto an integrating sphere which mixes the light. An optical fiber at the exit port of the integrating sphere transports the light to the tissue target. Yet another method is to utilize the waveguide effect of semiconductor and other materials.
There remains, however, a continuing need for improved light mixers for use with spectrophotometric instruments. A light mixer which can effectively mix narrow bandwidth light from several optical fibers would be desirable. To be commercially viable the light mixer should be capable of being efficiently manufactured.
The present invention is an improved light mixer structure for combining light from a plurality of individual optical fibers into a single optical transmission device. One embodiment of the light mixer structure includes a plurality of optical send fibers having input and output ends and an optical mixer having input and output ends. The output ends of the send fibers are in optical communication with the input end of the light mixer. The light mixer provides a high degree of light mixing yet is capable of being efficiently manufactured.